Now looking at the location of other parts - PSU, control box/board, water reservoir & pump and fume vent/fan. Checked up on the Duet 2 WiFi control board that I'm using for mounting and cooling advice.
My other printers currently have the board mounted vertically and open but I would prefer to have a box round the board for protection. Previously, I have had the board mounted in a box vertically with a fan behind it - so lots of cooling - but the orientation looked untidy and it was difficult to connect the wiring. I would prefer to have the board mounted (in a box) horizontally on top of the printer, though it could go on the side and vertically but again the connections would be awkward. Mounting the board horizontally with air blown across underneath the board seems overall best, I think.